The USB Device Smart Shopping Guide


Over the last few years, devices using USB ports have swept virtually all other connection types from store shelves - and that's a good thing. You no longer need to worry about choosing between serial or PS/2 mice, parallel port or SCSI scanners, parallel or serial printers - USB rules! However, there are still a few potential gotchas to consider when wading through holiday shopping crowds on a mission to pick up a USB device for your favorite computer user. These include:

  • - Bus-powered device blues
  • - Port-grabbing USB hard disks
  • - USB versus Hi-Speed USB hubs and devices

Beating the Bus-powered Device Blues

There are three places you can plug in a USB device:

  • - a USB port built into the system
  • - a USB port in a self-powered hub
  • - a USB port in a bus-powered hub

If you want to avoid problems, the first option's the best. With rare exceptions, USB ports built into your system provide a full 500 milliamps (mA) of power per port, the maximum power amount required for many of today's most popular USB devices like portable hard disks and flash memory. But, if you're short of USB ports, it's time for a hub.

Self-Powered Hubs Coming to an AC Outlet Near You

USB ports in a self-powered hub also provide a full 500 milliamps (mA) of power per port. By the way, the term "self-powered" is a bit of a misnomer: there are no atomic batteries or turbines inside a self-powered hub. Instead, a self-powered hub uses an AC adapter "briquette" that plugs into a wall outlet or surge suppressor. Most include four USB ports, but some include as many as seven.

'Bus-Powered' Means Low-Powered

A bus-powered hub might seem easier to use, because it doesn't use an AC adapter. Unfortunately, because it is powered by the upstream USB port, a bus-powered hub provides only one-fifth the power of a self-powered hub: just 100 milliamps (100mA) per port.

100mA is enough power to run most mice and keyboards, as well and devices with their own AC power source, such as 3.5-inch external hard disk drives, printers, and scanners. However, guess what USB devices are most likely to be stocking stuffers this year? USB flash drives and 2.5-inch hard disks! They need 500mA of power to run. A well-behaved device will complain (via the notification area) if there's not enough power, but I have seen a USB flash drive contents destroyed by plugging it into a bus-powered USB hub. Ouch!

Power Check, Power Check, 1-2-3-4...

By the way, if you're wondering how much power your USB devices use in Windows, open Device Manager and expand the Universal Serial Bus controllers category. Open the properties sheet for each USB Root Hub and Generic USB Hub, click the Power tab, and you will see the power usage for each device and the amount of power available per port. Some devices don't draw much power, and are happy with any type of a USB connection:

However, portable USB drives and flash memory devices top the list of power-hungry devices that expect a full 500mA of power on the USB banquet table:

To learn how to cope with reduced root hub power on some systems, read on.

What's With the Y-Cable on Some Portable USB Hard Disk Drives?

Portable USB hard disk drives are based on power-sipping 2.5-inch disk drive mechanisms, so, unlike their bulkier (and higher-capacity) 3.5-inch USB drive siblings, they can be powered off the USB bus. Ideally, a single USB port should do the job. However, because some systems don't provide a full 500mA of power per USB port and some hard disks require more power (up to 1000mA in some cases) to spin up, many portable drives include (or offer as an option) a two-port USB cable. In most cases, the power/data USB connector on the cable does the job, but on a system with low-powered USB ports, plug in the second power-only connector, and you're in business. See the review at right of a Seagate 40GB USB hard disk to learn more about this method.

Alternatives to Borrowing an Additional USB Port

Some drives, such as Verbatim 's SmartDisk product line, include a piggyback cable that plugs into a PS/2 mouse or keyboard port to provide additional power for a bus-powered hard disk. Some 2.5-inch hard disk enclosures also use this method. If your system has unused PS/2 ports and a shortage of USB ports, you might prefer one of these to a portable hard drive that uses a USB Y-cable (the method used by Seagate , Maxtor , and Hitachi , and offered as an option by Western Digital via its online store).

USB 1.1, the Standard That Will Not Die...but Why?

Believe it or not, the original 12Mbps USB 1.1 standard is still alive and well, at least in the external hub market. The only USB devices that won't care if you plug them into a USB 1.1 or USB 2.0 port are input devices such as mice and keyboards. If you plug any of today's USB hard disks, printers, flash drives, card readers, scanners, and so forth into a USB 1.1 port, you will slow them down from the 480Mbps transfer rate enjoyed by Hi-Speed USB (aka USB 2.0) devices to USB 1.1's feeble 12Mbps transfer rate. You'll get very sleepy waiting for your picture to print or files to transfer at 12Mbps!

Who's Selling USB 1.1 Hubs?

Big-box electronics retailer Circuit City is selling a Belkin USB 1.1 hub for $5.99 today, and Staples is offering a $9.98 Targus USB 1.1 mini hub this weekend. - but no amount of savings can make up for stifling the performance of your USB 2.0 devices by plugging them into a USB 1.1 hub. To make matters worse, these hubs don't include external power supplies, so they can't support devices that require more than 100mA per port.

USB 1.1 devices like these are gifts that keep on giving...frustration.

Making Sure You Don't Get Suckered by a USB 1.1 Device

There are other types of USB 1.1 devices stores are anxious to unload this holiday season. To make sure you don't get suckered, make sure hubs, card readers, and other USB devices are identified as supporting Hi-Speed USB or USB 2.0. A device identified as "USB" is probably a slooow USB 1.1 device.

Buy Smart - and Keep Your Receipts in Case You Goofed

So, as you review the Friday morning's doorbuster deals you scarfed up and prepare to go out again for more holiday shopping deals, keep an eye on USB device speeds and power requirements. Don't feel bad if you picked up a device that won't work the way you intended. After all, that's what receipts and return lines are for.

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